The invention relates to a wireless local area network (WLAN), and more particularly, to a power saving method for a station in the WLAN.
This section is intended to introduce the reader to various aspects of the art, which may be related to various aspects of the invention, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of related art.
For a WLAN station operating in a power saving mode, when no packet is received or transmitted (hereinafter referred to as a sleep period), components of the WLAN station are turned off to reduce current consumption. In order to receive a scheduled packet, components of the WLAN station are wakening up before the scheduled packet arrives. For example, during a sleep period, most components, except a control IC, of the WLAN station are turned off to reduce current consumption. In order to receive a scheduled packet, a voltage regulator and an oscillator circuit of the WLAN station are wakening up before the scheduled packet arrives.
FIG. 1 illustrates a schematic diagram of part of a conventional WLAN station. As shown in FIG. 1, in the WLAN station, a control IC 10 comprises one single enable pin 101 to simultaneously control both a LDO (low dropout) regulator 15 and an oscillator circuit (OSC) 17, where the LDO 15 supplies power to the OSC 17. For improving power efficiency, during the period where there is no data transmission to or from the WLAN station, the WLAN station will shut down almost every components and switch to a power saving mode. When the WLAN station operates in the power saving mode, control IC 10 will disable both the LDO 15 and the OSC 17, but keep itself idle in a sleep mode. On the other hand, when data transmission is initiated, control IC 10 will enable both the LDO 15 and the OSC 17 and keep itself back to an active mode. In the power saving mode, by disabling the LDO regulator 15, possible current leakage may be prevented, resulting in less power loss. However, disabling the OSC 17 in the power saving mode might worsen the power consumption. This is because, while switching back to the active mode, as the OSC 17 is enabled after the LDO 15 is enabled and starts to supply power to OSC 17, it takes lots of time for the oscillator circuit (OSC) 17 to achieve stable operation where possible abnormal high current consumption may occur thereby. More time it takes, more current and power it wastes. In addition, a radio frequency (RF) circuit (not shown) may require being re-programmed, and additional current consumption may be incurred. As a result, the conventional circuit design as shown in FIG. 1 is not good enough.
FIG. 2 illustrates a schematic diagram of part of a conventional WLAN station. Similar to the circuit shown in FIG. 1, control IC 20 comprises one single enable pin 201. Here, the LDO 25 is however not controlled by Control ID 20, instead, it is always enabled. When the WLAN station operates in the power saving mode, control IC 20 will disable the OSC 27 and keep itself idle in the sleep mode. And, when data transmission is initiated, control IC 20 will enable the OSC 27 and switch itself back to the active mode. In this design, because the LDO 25 is enabled during the sleep period, current leakage might be incurred thereby. But, since the LDO 25 never stop supplying power to the OSC 27 so as to keep it power on, a relatively short time required for the oscillator circuit 27 to achieve stable operation, and abnormal high current consumption can thus be avoided.
For a long sleep period, mechanism of FIG. 1 is better than the mechanism of FIG. 2 for its low current leakage. For a short sleep period, however, mechanism of FIG. 2 is better than the mechanism of FIG. 1 for it requiring a short stable time.